Paper mills utilize large conveyor systems for transferring rolls, e.g., from the slitter to the packaging line, and further to the storage area. The transport system comprises, e.g., lamellar conveyors, car conveyors, ramps and a variety of equipment suited to the transfer of the rolls from one conveyor to the next and to packaging lines. Such transport equipment incorporates different types of pushers and stops employed for pushing the roll into rolling motion and then stopping the same in a controlled manner at a desired location. The most common type of a roll stop is an arm pivotally mounted at its one end and adapted for motion control by means of a pneumatic cylinder. Such a roll stop operates so that along with its rolling motion, the roll hits a contact roll mounted to the distal end of the stop arm and begins to swing the arm toward the direction of the roll motion. Simultaneously, the arm actuates a pneumatic cylinder equipped with an outlet throttle valve at that side of the cylinder actuated during the braking of the roll motion. The throttling action slows down the cylinder stroke rate, as well as thereby also the roll motion, whereby the roll motion is brought to a halt. The cylinder is returned to its home position by applying compressed air pressure to the other side of the cylinder. Such return stroke can also be utilized for pushing the roll into a new motion, e.g., away from a wrapping station.
Conventional roll stops are operated at an almost constant rate of speed deceleration throughout the entire roll stopping distance. Currently, the size difference between the minimum size and maximum size paper rolls produced in paper mills is very large; in modern mills ranges typically are as wide as 200 . . . 8000 kg. A pneumatic stop performs satisfactorily only over a restricted range of roll sizes. When several different roll speeds have to be managed, a separate valve with an individual throttling characteristic has been required for each preset stopping speed. During operation, the roll size is identified, after which a suitable valve/throttling combination is selected for use by an automation system. Obviously, the number of the valves is limited in order to avoid an excessively complicated and expensive construction of the equipment. Typically, three different valve/throttling combinations have been employed, whereby three speed ranges are selectable.
The operating principle of a constant rate-of-speed deceleration over the entire stopping distance, as employed in prior-art roll stops, has several disadvantages. The paper roll hits the contact roll of the stop arm extremely violently at the instant of first encounter, and the outer layers of the roll may become damaged and therefore unusable. These unusable portions become scrap and are discarded. The instant the roll hits the roll stop, the stop imposes a high impact energy on the roll that causes deformations and possibly even web tear. Moreover, such a conventional roll stop is slow in operation, because it operates with a constant rate of speed deceleration over the entire stopping distance. During the transfer of the rolls, the speed of the rolls must be kept low, since the braking power of the roll stops must be designed sufficiently weak to avoid damage to the roll. On the other hand, this results in a long transfer time of the rolls and reduces the speed of the transfer lines substantially. Furthermore, a great number of intermediate stops and roll retarders are necessary to control the speed of the rolling paper rolls.